a) Field of the Invention
The present invention relates to a manufacture method for a field emission element, and more particularly to a method of manufacturing a field emission element having a field emission cathode from the tip of which electrons are emitted.
b) Description of the Related Art
A field emission element emits electrons from a sharp tip of an emitter (electron emission cathode) by utilizing electric field concentration. For example, a flat panel display can be structured by using a field emitter array (FEA) having a number of emitters disposed on a support substrate. Each emitter controls the luminance of a corresponding pixel of the display.
In a field emission element, a gate electrode biased to a positive potential relative to an emitter is disposed near the emitter. This gate electrode applies an electric field to the tip of the emitter to emit electrons from the emitter.
Another gate electrode (converging electrode) is provided, if necessary, to converge electrons emitted from the emitter. When a negative potential is applied to this electrode, a repulsion force is exerted upon electrons emitted from the emitter and converges the electrons.
Wang et. al., "Novel Single- and Double-Gate Race-Track-Shaped Field Emitter Structures", Proc. IEDM, 1996, pp. 313-316 discloses a race-track-shaped field emission element having two laterally disposed gate electrodes (double gate).
FIG. 21 is a cross sectional view of a race-track-shaped field emission element having two laterally disposed gate electrodes. A post gate 100 in a central area applies an electric field to the tip of an emitter electrode 101 to emit electrons from the emitter electrode 101.
An outer second gate electrode 102 is provided to increase the intensity of the electric field near the tip of the emitter electrode 101 to lower the threshold voltage (at which the emitter electrode starts emitting electrons) between the post gate electrode and emitter electrode. With the element having such a structure, the distance between the emitter electrode and each gate electrode is determined by the thickness of each of insulating films 103 and 104 made of, for example, SiO.sub.2. Since the area of the emitter electrode is large, the density of emission current per unit area is small.
The vertical height of the emitter electrode 101 is susceptible to change greatly depending on etching time and etching conditions. If the unevenness in the vertical heights of emitter electrons of manufactured elements is large, the performances of manufactured elements become very different.